Microstructure of YBa2Cu3O7-y films on CeO2-buffered Al2O3

We investigated the microstructure of epitaxial c-axis oriented YBCO films laser-deposited onto CeO2-buffered Al2O3 substrates. Using transmission electron microscopy (TEM), scanning electron microscopy and Auger electron spectroscopy, we have identified the majority of outgrowths which are spherical or polygonal in shape, with sizes ranging from 0.1 to 0.5 mum. as having the same composition as that of the YBCO matrix. Another type of outgrowth with irregular shapes and sizes ranging from 0.5 to 1.0 mum was also found to have a composition of BaCuO2 or CuO. Combined scanning transmission electron microscopy and selective area electron diffraction measurements identified the former as slightly misaligned YBCO. Although there is a large number of surface outgrowths in the YBCO film, the critical current density J(c) as calculated from hysteretic magnetization measurements is relatively high, where J(c) similar to 1.7 x 10(6) A cm(-2) at 77 K. (C) 2001 Elsevier Science B.V. All rights reserved.